$posts = get_posts(array(
'meta_query' => array(
'relation' => 'OR',
array(
'key' => 'colors',
'value' => 'red',
'compare' => 'LIKE'
),
array(
'key' => 'colors',
'value' => 'green',
'compare' => 'LIKE'
),
array(
'key' => 'colors',
'value' => 'blue',
'compare' => 'LIKE'
)
)
));